U.S. Pat. No. 4,397,270 discloses a variable valve timing and lift system. It includes a driving or shaft (which may be called a camshaft), a control shaft with axially spaced eccentric position controlling cams, and a pivot structure. The pivot structure supports valve operating (VO) cams for pivotal motion above valve lifters of cylinder valves. Springs are mounted for the VO cams, respectively. Each of the springs biases one of the corresponding rocker arms toward its rest position where the associated cylinder valve closes. Rocker arms operate the VO cams, respectively. The eccentric position controlling cams, which are in rotary unison with the control shaft, bear the rocker arms, respectively. An axis of each of the eccentric position controlling cams serves as the center of drive of the corresponding one of the rocker arms. Driver cams fixed to the driving shaft operate the rocker arms, respectively. An electronic control module (ECM) is provided. Sensors on the engine send information on engine speed, engine load, vehicle speed, and coolant temperature to the ECM. At a predetermined switchover point, the ECM sends a signal to an actuator for the control rod. As the actuator turns the control rod, the eccentricity of each of the eccentric position controlling cams with respect to an axis of the control shaft changes. This alters the position of pivot center of the rocker arms relative to the position of pivot center of the VO cams. This causes variation in valve timing and lift of each of the cylinder valves.
According to this known system, the camshaft is not mounted above the cylinder valves. This arrangement has a potential problem that the considerable modification of the conventional overhead camshaft engine is required to install the camshaft.
Co-pending U.S. patent applications Ser. Nos. 09/130,490 (filed on Aug. 7, 1998 by Seinosuke HARA et al.) now U.S. Pat. No. 5,988,125, and 09/219,774 (filed on Dec. 23, 1998 by Makoto NAKAMURA et al.) have been commonly assigned herewith and disclose various variable valve actuation apparatuses for Internal combustion engines.
GB 2 323 894 A, published on Oct. 7, 1998, discloses another type of variable actuation apparatus for an internal combustion engine.
The variable valve actuation apparatuses, which has been disclosed by the co-pending U.S. patent applications Ser. Nos. 09/130,490, 09/119,774 and GB 2 323 894 A are fairly well developed. However, a need remains for further development of such variable valve actuation apparatuses.